1. Field of the Invention
Embodiments of the present invention generally relate to sputtering targets used in electronic device manufacturing. In particular, the invention relates to bonding the sputtering target to a backing plate that supports the sputtering target in a deposition chamber.
2. Description of the Related Art
Physical vapor deposition (PVD) is one of the most commonly used processes in fabrication of electronic devices. PVD is a plasma process performed in a vacuum chamber where a negatively biased target is exposed to a plasma of an inert gas having relatively heavy atoms (e.g., argon) or a gas mixture comprising such inert gas. Bombardment (or sputtering) of the target by ions of the inert gas results in ejection of atoms of the target material. The ejected atoms accumulate as a deposited film on a substrate placed on a substrate pedestal disposed underneath the target within the chamber. Flat panel display sputtering is principally distinguished from the long developed technology of wafer sputtering by the large size of the substrates and their rectangular shape.
FIG. 1 (prior art) shows a typical DC magnetron PVD reactor 10, which includes an electrically grounded vacuum chamber 12 to which a target 14 is vacuum sealed through an electrical isolator 16. A DC power supply 18 negatively biases the target 14 with respect to the chamber 12 to excite an argon sputter working gas into a plasma. However, it is noted that RF sputtering is also known. The positively charged argon ions are attracted to the biased target 14 and sputter material from the target 14 onto a substrate 20 supported on a pedestal in opposition to the target 14. A magnetron 24 positioned in back of the target projects a magnetic field parallel to the front face of the target 14 to trap electrons, thereby increasing the density of the plasma and increasing the sputtering rate. In modern sputter reactors, the magnetron may be smaller and be scanned about the back of the target 14. Even a large magnetron may be scanned in order to improve the uniformity of erosion and deposition. Aluminum, titanium, and copper targets are typically formed of a sputtering layer of the material to be sputtered coated onto or bonded to a target backing plate of less expensive and more readily machineable material.
Sputter reactors were largely developed for sputtering onto substantially circular silicon wafers. Over the years, the size of silicon wafers has increased from 50 mm diameters to 300 mm. Sputtering targets need to be somewhat larger than the size of the wafers to provide more uniform deposition across the wafers. Typically, wafer sputter targets are formed of a single circular member for some materials such as aluminum and copper or a single continuous sputter layer formed on a backing plate for more difficult materials.
In the early 1990's, sputter reactors were developed for thin film transistor (TFT) circuits formed on glass panels to be used for large displays, such as liquid crystal displays (LCDs) for use as computer monitors or television screens. The technology was later applied to other types of displays, such as plasma displays, and solar panels, and on other panel compositions, such as plastic and polymer. Some of the early reactors were designed for panels having a size of about 400 mm×600 mm. Because of the increasing sizes of flat panel displays being produced and the economy of scale realized when multiple displays are fabricated on a single glass panel and thereafter diced, the size of the panels has been continually increasing. Flat panel fabrication equipment is commercially available for sputtering onto panels having a minimum size of 1.8 meter and equipment is being contemplated for panels having sizes of 2 m×2 m and even larger.
Due to the increasing sizes of panels, conventional way of bonding the sputtering targets to the backing plates by indium bonding is getting very expensive as the sputtering targets get larger and larger. Therefore, there is a need for a method of bonding sputtering targets to backing plates for large area substrate processing system that is economical and robust.